Tethyan Species Research Articles

Constraints on the expanse of Greater India in the Early Cretaceous from radiolarians

Defining the original size of Greater India is a critical parameter for reconstructing the kinematics and timing of the India–Asia collision. Early Cretaceous paleontology-based paleoceanographic and paleogeographic reconstruction for the northern coast of East Gondwanaland provides independent constraint for the extent of Greater India. In this study, newly discovered Early Cretaceous radiolarian faunas from the Tethys Himalaya were objectively compared with non-Tethyan austral faunas from the Argo Abyssal Plain (AAP) and the typical Tethyan fauna from Italy using the Hayashi's Quantification Method Type III. We found that (1) The occurrence of austral cold-water radiolarian species at the western coast of Australia and northern coast of Greater India is attributable to northward intrusion of circumantarctic cold water via a seaway newly opened during the breakup of East Gondwanaland from ∼136 Ma; (2) Gyangze was under shallow warm-water conditions with typical Tethyan radiolarian fauna (Cluster 3) until the late Valanginian when cold-water species (Cluster 1) arrived from the south. A water mass boundary shift from Tethyan species dominant to austral cold-water species dominant in Gyangze indicates its lower paleolatitude than Ocean Drilling Program (ODP) Leg 123, Site 765 in the AAP; (3) The same austral cold-water radiolarian-bearing intervals from the late Berriasian to Valanginian indicate that Kangma in southern Tibet was proximal to ODP Site 765; (4) Different radiolarian faunas in Italy–Zhongba, Kangma, and the AAP reveal complex water conditions under different degrees of effect by Tethyan warm water and austral cold water at different water depths during the Barremian to Aptian. This radiolarian biogeography is highly consistent with the paleomagnetic reconstruction and indicates that eastern Greater India extended to the Exmouth Plateau (>2400 km) during the Early Cretaceous.

Late Cretaceous larger rotaliid foraminifera from the westernmost Tethys

A detailed taxonomical study of the larger rotaliid foraminifera found in the Upper Cretaceous deposits from the External Prebetic Zones (SE Spain) has been carried out for the first time. The study of the samples has revealed the diversity and abundance of this foraminiferal group and its usefulness as a tool for regional biostratigraphy. Five new species and two new genera are described, Pseudosulcoperculina bocairentina gen. et sp. nov., Plumopraelockhartia solanensis gen. et sp. nov., Rotalia baetica sp. nov., Suturina minima sp. nov., and Neorotalia? pinetensis sp. nov. These and other species of larger benthic foraminifera have been found forming two different assemblages. The older assemblage, dated as middle to late Campanian, is composed of the rotaliid species N.? pinetensis sp. nov., R. baetica sp. nov., Suturina globosa, Rotorbinella sp., Pararotalia tuberculifera and Rotalispira scarsellai. The younger assemblage is dated as late Maastrichtian, including the rotaliids Pseudosulcoperculina bocairentina gen. et sp. nov., Plumopraelockhartia solanensis gen. et sp. nov. and Pararotalia tuberculifera. In global terms, the Late Cretaceous rotaliids from the Prebetic are key in our understanding of the phylogenetic relationships among the Cretaceous and early Paleocene Tethyan species, allowing to root the origin of the lockhatiines sensu lato back to the Upper Cretaceous. Besides, the new data regarding the Sulcoperculina-like forms have revealed the differences and similarities among the species of both sides of the Atlantic, especially, between the architecture of the American genus Sulcoperculina and that of similar forms in Pyrenean and Tethyan realms, grouped into new a genus here introduced as Pseudosulcoperculina.

On the co-occurrence of Rubroceras and Vascoceras (Ammonoidea, Vascoceratidae) in the upper Cenomanian of the West Portuguese Carbonate Platform

The upper Cenomanian and basal Turonian ammonite assemblages of the West Portuguese Carbonate Platform (WPCP) are characterised by the occurrence of many Tethyan species, with emphasis on Vascoceratidae. They include Vascoceras gamai, type-species of the genus, and several other taxa created in 1898, by Choffat, based on abundant materials collected from exposures of the Baixo Mondego region (West Central Portugal), in the northern range of the carbonate platform. As noted by Berthou et al., in 1975 and subsequent works, many of these Vascoceras are upper Cenomanian and form two distinct assemblages, respectively with Euomphaloceras septemseriatum and Pseudaspidoceras pseudonodosoides. The occurrence of this latter species can be correlated with the uppermost Cenomanian Neocardioceras juddii standard zone, since both species co-occur in assemblages with vascoceratid ammonites described by Cobban et al. (1989) in New Mexico (United States). It is precisely from the same assemblages that the genus Rubroceras was originally described, as an interesting example of the late Cenomanian evolutionary diversification of the Vascoceratidae, when highly ornamented forms with transverse ribs persisting in the body chamber appeared in Tethyan assemblages with Vascoceras, characterised by much more smooth morphologies.As in New Mexico, the occurrence of Rubroceras in the WPCP is restricted to a stratigraphic unit with Pseudaspidoceras pseudonodosoides, Vascoceras gamai, V. barcoicense and V. silvanense. Besides Rubroceras alatum and R. burroense, other additional taxa are Spathites (Jeanrogericeras) subconciliatus, Vascoceras adonense, Vascoceras sp. A and Parapuzosia (Austiniceras) sp. This assemblage mostly occurs in the outcrops of Nossa Senhora dos Olivais, near Tentúgal, in the northern range of the carbonate platform. It is found above beds with Euomphaloceras septemseriatum and Vascoceras gamai, and below the highest upper Cenomanian unit of the area, with P. pseudonodosoides, Spathites (Jeanrogericeras) subconciliatus, Fagesia catinus, and depressed Vascoceras, such as V. durandi, V. douvillei and V. kossmati.In addition to New Mexico and West Portugal, representatives of Rubroceras are presently known from other carbonate platforms of North Africa, Arabian Peninsula and Nigeria, where they have been found in ammonite assemblages correlative to the Neocardioceras juddii standard zone. They are apparently absent from the remaining basins of the Iberian microplate with abundance of Vascoceratidae representatives, namely the Iberian Through (Spain), whose late Cenomanian oceanic communication was more processed from the North. Further studies will provide a better understanding of this important biotic dispersal event across the Tethyan Realm, as an additional marker of uppermost Cenomanian ammonite assemblages.

A Revision of the Macraster species (Echinodermata, Echinoidea) occurring in the Albian deposits of the Zagros basin, Southwest Iran

The paper describes the spatangoid echinoids belonging to Macraster, which could be found in the Albian deposits (Kazhdumi Formation) at the Anneh anticline situated in Zagros Mountains, Southwest of Iran. The aim is to re-examine, and redefine three species: M. douvillei, M. longesulcatus and M. obtritus. Douvillaster and Macraster genera are synonymized and then the assignment of nominal Tethyan species belonging to the same genera is reviewed. The substantial reduction of species does not strongly impact the biodiversity patterns. Neither the bio-geographical provinciality nor the temporal trends of taxonomic richness are affected. Among the Cretaceous spatangoids, Macraster is a highly specialized taxon that displays outstanding adaptations of the ambulacra to improve in the gaseous exchanges. This, in return, triggers the higher frequency of the taxon in the warm shallow waters of the Tethyan margins, and in oxygen-depleted environments.

Diversity dynamics of ammonoids during the latest Bajocian and Bathonian (Middle Jurassic) in the epicratonic Polish Basin

Results of the analysis of Middle Jurassic (latest Bajocian–Bathonian) ammonoid diversity patterns in the Polish Basin are reported. The data used in this study are based on a large number of ammonoid specimens, collected bed-by-bed, from the Polish Jura in south-central Poland, as well as on existing literature. The ammonoid diversities, both at the genus and species levels, have been calculated for particular ammonite zones and subzones and compared with the regional transgressive–regressive cycles for the Polish Lowlands and Hallam’s global sea-level curve. The patterns of ammonoid diversity dynamics seem to be well correlated with global sea-level fluctuations. Particular diversity peaks correspond with major transgressive episodes. Three main regional bio-events related to transgressions have been distinguished for the Polish Basin: (1) the Latest Bajocian (Bomfordi Subchron) bio-event is related to a short-lasting immigration of Tethyan ammonoids; (2) a late Early Bathonian (Tenuiplicatus Chron) bio-event corresponds to a proliferation of Asphinctites tenuiplicatus (Brauns), most probably as a result of transgression-driven eutrophication of a shallow-marine environment; during this time, the immigration (passive dispersion?) of some single Tethyan species is also observed; and (3) a Late Bathonian (Hodsoni and Orbis chrons) bio-event corresponds to the highest ammonoid species diversity peaks and most probably is related to the major transgression during the Bathonian, which allowed easy migration of several species via several newly opened sea-ways.

Early Cretaceous dinoflagellate cysts from the southern border of the Neuquén Basin, Estancia Santa Elena locality, Argentina*

� � � � � � � p� � � � w� � � � ��� � � An assemblage of dinoflagellate cysts is reported from the Lower Member (Pilmatué Member) of the Agrio Formation (late Valanginian-Hauterivian) of the southern Neuquén Basin, Argentina. Thirty species are recognized and the new w species Oligosphaeridium quattrocchioae and Muderongia sarjeantii described. The studied assemblage is compared w with other Early Cretaceous assemblages from central w western Argentina, Patagonia, the South Atlantic Malvinas Plateau, the Antarctic Peninsula and Australia. The marine dinoflagellate cyst assemblage of the Agrio Formation at the Estancia Santa Elena locality has cosmopolitan character, w with a p predominance of European and Tethyan species.

The Early Cretaceous of North-East Greenland: A crossroads of belemnite migration

Recent field work in Lower Cretaceous successions of Traill Ø and Wollaston Forland, North-East Greenland, have resulted in c. 2350 belemnite guards collected bed-by-bed from the upper Ryazanian – Hauterivian. The most common belemnite genera observed, Acroteuthis, Pachyteuthis, and Cylindroteuthis are of boreal-arctic affinities and closely related to NW European and Siberian faunas. Other taxa, including Hibolithes (common), Pseudobelus (relatively common) and Duvalia (rare), show faunal links to both NW European and Mediterranean faunas. This paper describes and discusses these findings in their taxonomic, biostratigraphic, palaeobiogeographic, palaeoecologic and palaeoceanographic context. In particular, the occurrence of Pseudobelus which is common in the circum Mediterranean area, is remarkable since it is the first observation of this Tethyan genus in the entire Boreal Realm. The palaeoecological interpretation of these observations result in the recognition of four different palaeobiogeographic belemnite assemblages for the Boreal Realm: 1) North-East Greenland, 2) Spitsbergen, 3) NW Europe and 4) Siberia. In contrast to the other assemblages, the belemnite faunas of North-East Greenland consist of a) Boreal-Arctic elements, b) Boreal-European taxa, c) endemic belemnites of Tethyan ancestry, and d) Tethyan species. These findings make North-East Greenland part of an immigration route from the Tethyan Realm via the north Atlantic to the high Boreal. This allowed Tethyan species, which are otherwise unknown from the Boreal Realm, to reach North-East Greenland. The occurrence of the Tethyan genus Pseudobelus in North-East Greenland also supports the interpretation of this taxon as a hemipelagic dweller, capable of crossing major distances. The belemnite patterns further suggest the existence of a proto Gulf-stream, documenting a south-to-north flow of warm surface waters as far north as Greenland already in the earliest Cretaceous (Valanginian). This has substantial implications for the interpretation of Early Cretaceous climate and oceanic current systems, as well as for the palaeobiology of belemnites.

MIDDLE TRIASSIC PTERIOMORPHIAN BIVALVIA (MOLLUSCA) FROM THE NEW PASS RANGE, WEST-CENTRAL NEVADA: SYSTEMATICS, BIOSTRATIGRAPHY, PALEOECOLOGY, AND PALEOBIOGEOGRAPHY

The parautochthonous Anisian and Ladinian rocks of the New Pass Range previously referred to as the Augusta Mountain Formation have a unique, endemic assemblage of pteriomorphian bivalves with Triassic Northern Hemisphere biogeographic relationships, especially to the Carnian cratonal faunas of northeastern British Columbia as well as to Ladinian faunas of the Shoshone Mountains and the Gillis Range. A new suborder Prospondyloidina is described, as well as three new genera, Promysidiella, Loxochlamys, and Nevadapecten, a new subgenus, Gervillaria (Baryvellia), and 17 new species either named or referred to by letters: Promysidiella planirecta, P. desatoyensis, Bositra favretensis, Enteropleura species a, Gervillaria (Baryvellia) ponderosa, Atrina sinuata, Antiquilima ladinica, Palaeolima newpassensis, Plagiostoma acutum, Leptochondria shoshonensis, Asoella? species a, b, and c, Oxytoma (Oxytoma) grantsvillensis, Pleuronectites newelli, Loxochlamys corallina, and Nevadapecten lynnae. Promysidiella aff. otiosa is a new combination for Mytilus otiosus McLearn; Mysidiella newtonae n. sp., Norian, Wallowa terrane, is based on Krumbeckiella cf. timorensis (Krumbeck) of Newton, 1987. Triassic “Posidonia” is placed in Bositra de Gregorio, 1886, regarded as a senior synonym of Peribositria Kurushin and Trushchelev, 1989. The morphological and stratigraphic sequence Bositra-Enteropleura-Daonella-Aparimella-Halobia is rooted in Paleozoic Caneyella and Posidonia and indicates declining dependence on and eventual loss of byssal attachment as well as a possible shift from low to high dispersal ability (between Bositra and Enteropleura). There is no evidence for trans-Panthalassan dispersal of bivalves in low latitudes within the interval of Ladinian coral beds. So-called Tethyan and Muschelkalk species are endemics in slowly evolving genera or are phylogenetically convergent on west Tethyan species.

Controls on migration of conodont fauna in peripheral oceanic areas. An example from the Middle Triassic of the Northern Peri-Tethys

Middle Triassic conodont assemblages in the semi-closed Peri-Tethyan Germanic Basin comprise endemic forms, which evolved within the basin, and immigrants from the Tethys Ocean. Migration from the Tethys proceeded diachronously through three tectonically predisposed pathways (gates) and was controlled by relative sealevel changes recorded in depositional sequences of the Muschelkalk. In the Early and Middle Anisian predominant were the forms that originated in the Eastern Tethys and in southern basins of the Western Tethys. They migrated through the East Carpathian Gate and Silesian-Moravian Gate. In the late Anisian and early Ladinian forms from the Western Tethyan basins prevailed; their migration pathway led through the Western and East Carpathian Gates. The latter gate was active only at the turn of Illyrian and Fassanian. Episodes of migration of the Tethyan forms and dispersal of conodont fauna throughout the German Basin coincide with the transgressive or highstand phases of a particular depositional sequence (as defined by Szulc, 1999). The most significant proportion of the Tethyan species appears to correlate with the maximum flooding surface of the A 3 sequence, (Lower Muschelkalk) later they decrease in diversity. In the Upper Muschelkalk the most numerous Tethyan species correspond to the transgressive phase of the L 1 sequence. Above the mfs of the L 1 sequence only the Germanic forms remain.

Late Palaeocene–Early Eocene dinoflagellate cysts from the Turgay Strait, Kazakhstan; correlations across ancient seaways

The results of a quantitative palynological analysis, emphasizing organic-walled dinoflagellate cysts (dinocysts), of Palaeocene–Eocene deposits exposed in the Sokolovsky Quarry (Turgay Trough, Northern Kazakhstan) are presented here. Located in the ancient Turgay Strait, a former seaway presumed to have connected the Tethyan and Boreal oceans and seas in the early Palaeogene, the Sokolovsky Quarry outcrop occupies a key position for the analysis of connections between these realms.In general, the dinocyst succession of Sokolovsky closely resembles coeval Arctic Ocean–North Sea Basin counterparts; only in one interval endemic and/or possibly Tethyan species co-occur. The successive dinocyst assemblages allow recognition of the Late Palaeocene–Early Eocene P5a, P5b, P6a, P6b and E2 zones established in the North Sea Basin. The succession is interpreted to represent parts of several third-order sea level cycles correlative with those recognised in the North Sea Basin. Detailed comparison with similar studies from southeastern England allows the recognition of (parts of) third order cycles Thanetian-1 (Tht-1), 2, 4, 5, and Ypresian (Ypr)-3. In addition, two important stratigraphic gaps within the Palaeocene–Eocene succession are recognised, possibly reflecting times of sea level lowering. These gaps are inferred from (1) the absence of a complete P5b/P6a transition, (2) the absence of zone E1, and (3) (bio)sequence stratigraphy.Combined results indicate that the Turgay Strait flooded from the north between ∼57.8 and 57.1Ma (cycles Tht-1 and 2, in part, with a minor missing section). During the ‘second’ phase of Turgay-flooding (∼56.4–55.3Ma), evidence may be taken to indicate increased influence from the Tethyan Ocean and/or warmer conditions. Deposits reflecting the Late Palaeocene Thermal Maximum, associated with this interval, are present at Sokolovsky Quarry. This interval is marked by abundant Apectodinium spp., including A. augustum, and organic-rich layers. A third flooding is correlative to the London Clay transgression (from ∼54.5Ma).From our study, no decisive evidence has become available that confirms that a connection between the Arctic and Tethyan oceans via the Turgay Strait in the early Palaeogene existed. Nevertheless, during intervals of major sea level fall, the Turgay Strait depression may be regarded to have been an important feature for migrating terrestrial biota.Four new wetzeliellioid taxa Apectodinium sp. A, Apectodinium sp. B, Wilsonidium? sp. A and Wilsonidium? sp. B are described from the Palaeocene part of the section.

Benthic foraminifera: indicators for a long-term improvement of living conditions in the Late Valanginian of the NW German Basin

Abstract. Foraminiferal occurrences in marine sediments of Late Valanginian age (Early Cretaceous) are described from NW Germany. The distribution patterns of benthic foraminifera are discussed with respect to their abundance and diversity. Benthic foraminifera are characterized in terms of moderate diversity and abundance. Vertical fluctuations in foraminifera contents are discussed with respect to their palaeoecology and palaeobiogeography. Benthic foraminifera, which are represented by a total of 101 species, show a gradual increase of diversity throughout the Late Valanginian. This improvement of living conditions in an epicontinental sea over a period of approximately 2 million years indicates a gradual recolonization of the formerly non-marine semi-restricted basin. The associations are dominated by agglutinated taxa with common Ammobaculites, Ammovertella, Bulbobaculites, Haplophragmoides, Proteonina, Psammosphaera and Reophax. The calcareous species Epistomina caracolla, which is extremely common in certain intervals, may reach significant abundances. Further agglutinated and calcareous taxa occur rarely. The early Late Valanginian is marked by the occurrence of the Tethyan species Cerobertinella subhercynica, reflecting a major sea-level highstand.

New Early Permian fusulinid assemblage from Guatemala

Abstract A Latest Sakmarian–Earliest Artinskian (i.e. Late Wolfcampian) fusulinid assemblage, mainly composed of Levenella (?) and Pseudofusulinoides , has been discovered in the Purulha area, Guatemala. It contains some Tethyan species never described in America, mixed with more classical cratonic North American species. Palaeobiogeographically, this association allows improved correlations between the American and Tethyan faunistic provinces, and provide evidence of repetitive fusulinid and alga migrations during the Permian through Palaeopacifica, from the eastern Asian Blocks to the Chortis Block.

Middle Permian brachiopods from central Peninsular Malaysia — faunal affinities between Malaysia and west Cambodia

A moderately diverse Permian brachiopod fauna is described from a new rock unit, the Bera Formation, in the Bera District, central Pahang, Peninsular Malaysia. The fauna consists of 19 taxa, including 14 genera and 17 (both identified and unidentified) typically Tethyan species. The fauna appears to be correlative on the basis of brachiopods with the Neoschwagerina-Yabeina fusulinid Zones in Indochina and South China. In particular, it has strong linkage to Member C ( Yabeina beds) of the Sisophon Limestone, west Cambodia. This is indicated by three of the Bera species — Urushtenoidea chaoi (Ching), Spyridiophora gubleri Termier and Termier, and Transennatia termierorum sp. nov., being shared with the Cambodian fauna. A possible early Capitanian (Middle Permian) age is proposed for the Bera brachiopod fauna.

Biogeography and diversity of South Atlantic Cretaceous echinoids: implications for circulation patterns

This survey of echinoid species living on the African and South American margins of the South Atlantic Ocean in Cretaceous times is based on a review of published species and abundant unpublished material. The synthetic approach is used to ascertain how the South Atlantic was colonised by echinoids from the time it first opened in the Early Cretaceous until communications were established with the North Atlantic and Mediterranean–Tethys in the Late Cretaceous. The survey focuses on the biogeographical origin of immigrant species and their relations with Indo-Madagascan, North Atlantic and Mediterranean–Tethyan faunas. Qualitative variations in species diversity are also studied where available fossil material permits, together with the in situ evolution of certain lineages and their endemism. Finally, echinoid colonisation of the South Atlantic during the Cretaceous is viewed against palaeocurrent patterns. The survey shows, within the limits of material available, that no echinoid fauna attests to the existence of the narrow marine trough separating South America and Africa in the Barremian. In the Aptian, West African echinoids display a Mediterranean–Tethyan influence, indicating a probable link between south-east and west of Africa via the strait opened between Africa and Madagascar. Echinoid fauna on the Brazilian margin includes species found in what is now continental North America and on the Pacific seaboard of South America. During the Albian, South America separated completely from Africa and normal marine communications were established with the Western Tethys to the north and the Southern Ocean domain to the south. The echinoid fauna of the South Atlantic during the Albian and early Cenomanian was particularly rich and diversified, with the earliest ubiquitous species on both margins of the ocean. In the late Cenomanian–early Turonian, a Tethys–South Atlantic Ocean link probably formed in West Africa through the Sahara and Nigeria, favouring the influx of Mediterranean–Tethyan species to the South Atlantic. During the mid Turonian–Coniacian, the trans-Saharan channel closed, slowing down colonisation of the South Atlantic by Mediterranean–Tethyan echinoids, as the only connection was via the Central Atlantic. This period was marked by the stability of a number of lineages that survived without major morphological changes in areas colonised during Cenomanian times. In the late Senonian, the South Atlantic was largely open to the neighbouring ocean domains and a new trans-Saharan channel linked the Mediterranean–Tethys and South Atlantic directly. This allowed substantial faunal exchanges and most Senonian echinoids found on the South Atlantic rim are common to both its eastern and western margins.

Jurassic ammonite faunas from Nepal and their bearing on the palaeobiogeography of the Himalayan belt

From the Upper Bathonian up to the Tithonian–Berriasian, six main faunas and twelve basic faunal assemblages within them are distinguished in Nepal. The successive faunas show (1) low taxonomic diversity and (2) the dominance of a small number of genera and the subordinate place of the associated taxa. The assemblages include: (1) strictly Tethyan (e.g., Mediterranean or European Tethyan) species and/or genera, very few in number and occurring as isolated individuals or discontinuous faunal horizons; (2) Indo-Malagasian components, some scattered, others with a wide occurrence in the SW Pacific, some as far as Antarctica and/or Patagonia; (3) indigenous genera endemic for the Himalayas and the SW Pacific region. Faunas of the same age for the Sula Islands, Papua-New Guinea, Australia, New Zealand, Antarctica and South America are also considered. In spite of common components, the Himalayan faunas contrast with the relatively higher diversity of the Indo-Malagasian faunas. Low diversity and dominance of indigenous genera mean that the faunas extending from the Himalayas to Antarctica and Patagonia represent an actual biogeographical unit, the Indo Pacific (faunas and) Realm. Indo Pacific and Tethyan faunas show a less marked contrast than the Tethyan and Boreal. Transitional or mixed faunas of subaustral type developed in the Indo-Malagasian and Andean regions. This is explained by the absence of a geographical trap comparable to the land-locked palaeogeography of the Arctic Basin. The palaeogeography of the Arctic amplified the role of the other environmental factors. Among these the high latitude seasonal effects are likely to have resulted in environmental instability, controlling trophic resources and therefore the structure of the ecosystems, for instance low diversity and high density of the high latitude ammonite faunas.

Zoogeography of Holocene Podocopina (Ostracoda) from the Brazilian Equatorial shelf

This study reports on the Holocene ostracods of the Brazilian Equatorial shelf from French Guiana to near Natal, almost 1400 km in length. This part of the Western Atlantic Tropical Province, where the mouths of the Amazon and Pará rivers separate two zoogeographical units, has distinct oceanographic and sedimentologic features. Three hundred and thirty nine samples were studied from the REMAC (legs 4, 5, 5A and 6) and the GEOMAR projects (legs I, II and III). The ostracod fauna includes 74 species, of which 37 have been previously described (mostly from other areas). The remaining 37 species are left in open nomenclature although 26 of them are probably new. Twelve species are confined to the northwest and 16 to the southeast of the mouths of the Amazon and Pará rivers. The inner shelf of the northwestern region is a barren zone resulting from turbid freshwater discharged by the Amazon and Pará rivers. Most of the studied species live at water depths of less than 100 m; 28 species inhabit waters shallower than 75 m, and 18 species live in waters shallower than 50 m. Although Brazilian ostracods have many genera and species in common with Holocene ostracods elsewhere in the tropical Atlantic, diversity differs greatly. For example, diversity on the Brazilian Equatorial shelf is lower than elsewhere in the Western Atlantic Tropical Province, but higher than in the Eastern Atlantic Tropical Province. Faunal similarities between these provinces are at the generic rather than species level; exceptions are few and consist of conservative Tethyan species that are cosmopolitan.

New radiolarians from the earliest Cretaceous of the Sultanate of Oman (Wahrah Formation, Jebel Buwaydah)

In a section from the central Oman Mountains (Wahrah Formation, Jebel Buwaydah) well preserved radiolarians were extracted. Stratigraphically they represent typical earliest Cretaceous species (Bernasian). Besides well known Tethyan species allowing an exact age determination, unknown morphotypes are common in some samples. Some of these represent new species, which are described herein. The composition and diversity of the faunas hints to a depositional environment in the lower bathyal.

Early Cretaceous radiolarians of the Northeast Indian Ocean (Leg 123: Sites 765, 766 and DSDP Site 261): The Antarctic-Tethys connection

During ODP Leg 123, abundant and well-preserved Neocomian radiolarians were recovered at Site 765 (Argo Abyssal Plain) and Site 766 (lower Exmouth Plateau). Assemblages are characterized by the numerical dominance of a small number of non-tethyan forms and by the scarcity of tethyan taxa. Remarkable contrasts exist between radiolarian assemblages extracted from claystones of Site 765 and reexamined DSDP Site 261, and faunas recovered from radiolarian sand layers, only found at Site 765. Clay faunas are unusual in their low diversity of apparently ecologically tolerant (or solution resistant?), ubiquist species, whereas sand faunas are dominated by non-tethyan taxa. Comparisons with Sites 766 and 261, as well as sedimentological observations, lead to the conclusion that this faunal contrast resulted from a difference in provenance, rather than from hydraulic sorting or selective dissolution. The ranges of 27 tethyan taxa from Site 765 were compared to the tethyan radiolarian zonation by Jud (1992) by means of the Unitary Associations Method. This calculation allows to directly date the Site 765 assemblages and to estimate the amount of truncation of ranges for tethyan taxa. Over 70% of the already few tethyan species of Site 765, have truncated ranges during the Valanginian-Hauterivian. Radiolarian assemblages recovered from claystones at Sites 765 and 261 in the Argo Basin apparently reflect restricted oceanic conditions during the latest Jurassic-Barremian. Neither sedimentary facies nor faunal associations bear any resemblance to what we know from typical tethyan sequences. We conclude that the Argo Basin was paleoceanographically separated from the Tethys during the Late Jurassic and part of the Early Cretaceous by its position at higher paleolatitudes and/or by enclosing land masses. Assemblages recovered from radiolarian sand layers are dominated by non-tethyan species that are interpreted as circumantarctic. Their first appearance in the late Berriasian-early Valanginian predates the oceanization of the Indo-Australian breakup (M11, late Valanginian), but coincides with a sharp increase in margin-derived pelagic turbidites. The Indo-Australian rift zone and the adjacent margins must have been submerged deeply enough to allow an intermittent influx of circumantarctic cold water into the Argo Basin, creating increased bottom current activity. Cold-water radiolarians carried into the Argo Basin upwelled along the margin, died, and accumulated in radiolarite layers due to winnowing by bottom currents. High rates of faunal change and the sharp increase of bottom current activity are thought to be synchronous with possible pronounced late Berriasian-early Valanginian lowstands in sea level. Hypothetically, both phenomena might have been caused by a tendency to glaciation on the Antarctic-Australian continent, which was for the first time isolated from the rest of Gondwana by oceanic seaways as a result of Jurassic-Early Cretaceous sea-floor spreading. The absence of most typical tethyan radiolarian species during the Valanginian-Hauterivian is interpreted as reflecting a time of strong influx of circumantarctic cold water following oceanization (M11) and rapid spreading between Southeast India and West Australia. The reappearance and gradual abundance/diversity increase of tethyan taxa, along with the still dominant circumantarctic species are thought to result from overall more equitable climatic conditions during the Barremian-early Aptian and from the establishment of an oceanic connection with the Tethys Ocean during the early Aptian.

Late Lower Kimmeridgian-Lower Tithonian Virgatosphinctins of India: Evolutionary succession and biogeographic implications

A very significant late Lower Kimmeridgian to Lower Tithonian virgatosphictin ammonoid fauna is examined under the rigorest possible stratigraphic precision at Ler-Katrol (Kachchh), India for evolutionary succession and biogeographic implications. The study allows the recognition of at least 12 successive faunas which have been organised into 8 zones and 12 subzones along with their relative precise correlations with Western Tethys. The principal single lineage worked out is Torquatisphinctes intermedius (Alterneplicatus Zone to Acanthicum Zone)— Pachysphinctes bathyplocus (Bathyplocus Zone)— Katroliceras katrolensis (Katrolensis Zone) (up to close of Kimmeridgian)— K. pottingeri (Pottingeri Zone). K. pottingeri in turn gives origin by cladogenesis to two short lived lineages, which include new species one in each lineage marking the termination of the stock at the close of Lower Tithonian with a probable lineage discontinuity in the basal Tithonian Hybonotum Zone. Among the other salient features are: 1. There is a major stratigraphic break at the base (=Vail's subcycles LZA 4.3–4.4). The start of the fauna corresponds to the eustatic rise of LZA 4.5, while the termination of the lineage is correlated with the termination of LZB 1.1. 2. K. pottingeri, known widely in the Indo-East-African province, is precisely dated for the first time as post—Hybonotum Zone, in association of very significant although also not well dated Himalayan Aulacosphinctoides (A. uhligi, A. willisi, A. tibetanus etc.). Aulacosphinctoides in the section is also found older than Virgatosphinctes. 3. The rare presence of non-virgatosphinctin West Tethyan species indicates expansion events related to eustatic rises, which permits correlation with the Western Tethys of the otherwise near endemic Indian faunas. Nothing is found in common with the SE. Pacific faunas, suggesting continued absence of a direct marine connection via the east and south coastal region of Africa.

Paleocology of late Maastrichtian Heterohelicidae (planktic foraminifera) from the Atlantic region

Late Maastrichtian planktic foraminiferal Heterohelicidae from Deep Sea Drilling Project sites in the northwestern Atlantic (111 and 605), the South Atlantic (356 and 357), and from Mediterranean land sections near E1 Kef (Tunisia) and Caravaca (Spain) show two bioprovinces. Site 111 has Transitional heterohelicid faunas, in which a few Heterohelix species dominate, while the other localities have diverse Tethyan faunas. A quantitative analysis allows for a more detailed subdivision within the Tethyan faunas. Heterohelicid species occur in different relative frequencies at the South Atlantic, the North Atlantic, and the Mediterranean localities. The South Atlantic DSDP Sites contain Heterohelix rajagopalani (Govindan) in addition to all other Tethyan species. The faunas from the two Mediterranean sections are comparable. However, the overall diversity at El Kef is the lowest of all Tethyan sections, and the area is interpreted as representing paleo-upwelling. The otherwise diverse faunas from the North Atlantic Site 605 contain some Transitional elements, which suggests mixing with cooler surface waters, possibly derived from a proto-Labrador Current.